The present invention relates to copolymer dispersions having excellent particle size distribution and to polyurethanes prepared by reacting these dispersions with reactive polyisocyanates.
Polyurethanes constitute a broad class of polymeric materials having a wide range of physical characteristics. The polymers are produced by the reaction of a polyisocyanate with a polyfunctional compound having an active hydrogen in its structure. This active hydrogen compound is generally a liquid or solid capable of being melted at relatively low temperatures. Most commonly, the active hydrogen compound contains hydroxyl groups as the moieties having the active hydrogen and thus are termed polyols, e.g., the polyols of polyesters, polyester amides, or polyethers, or mixtures of two or more such materials. For reasons of commercial availability and cost, the polyols most commonly employed in the preparation of polyurethanes are the polyethers having hydroxyl terminated chains and hydroxyl terminated polyesters.
Although a wide variety of physical and chemical properties are obtainable by the proper selection of a polyisocyanate and the polyol as well as the conditions under which the polyurethane reaction is carried out, the resulting polyurethane often exhibits properties such as load bearing and processability, particularly foam applications, unacceptable for some applications.
To improve such properties, it has been the practice of the art to employ graft copolymer dispersions (often called polymer polyols) prepared from vinyl monomers and polyols in the preparation of polyurethanes as shown in U.S. Pat. Nos. 3,383,351; 3,304,273; 3,523,093; 3,652,639 and 3,823,201. In 3,304,273, a mixture of styrene and a polar monomer are copolymerized while dispersed in a polyol which is essentially free of ethylenic unsaturation. Unfortunately, stable dispersions cannot be prepared by this technique if high proportions of styrene monomer are employed. Subsequently, in order to overcome this problem, it was found desirable to employ polyols which contain a significant amount of ethylenic unsaturation. As shown in U.S. Pat. No. 3,823,201, such unsaturation was advantageously introduced by reacting the polyol with an organic compound having both ethylenic unsaturation and hydroxyl, carboxyl or epoxy moieties which are reactive with the active hydrogen moiety of the polyol. While these more improved graft copolymer dispersions solve many of the problems confronting the polyurethane art, more efficient control of particle size of the disperse phase is desired for many applications.
Accordingly, it is highly desirable to provide an improved, low viscosity copolymer dispersion wherein less unsaturated moiety is required in the polyahl in order to achieve the desired particle size and particle size distribution in the dispersion.